config.guess sets SUN_ARCH to ‘x86_64’ only if preprocessor defines ‘__amd64’ - however, the config.guess script does not use the CFLAGS passed (which actually sets -m64) for this preprocessor check and hence the build host is not
set correctly.

Passing an explicit “--build=x86_64-pc-solaris2.10” to the configure script or setting CC=”<compiler> -m64” solves the issue.